The lifecycle of reinforced concrete structures in marine environment depends on many factors such as the properties of structures (concrete strength, permeability, corrosion resistance, type of cement, mixtures.etc), environmental effects (temperature, wet/dry cycle, chloride concentration), design, construction quality, construction management and exploitation methods.etc. Lifecycle prediction based on life cycle computation theory or software is an essential process when designing. This article presents the lifecycle forecasting results of reinforced concrete constructions in Hai Phong’s sea using Life-365 software, the initial results show that the corrosion beginning time of reinforced concrete constructions in Hai Phong's sea is pretty soon. And, the study also proposes the use of Life-365 software as a tool for planning project life.